With yesterday’s announcement that Sam Raimi’s Spider-Man 4 will not start production in time for its planned May 5, 2011 release, other studios are looking to grab some of those dates for their own tentpoles. Making that rumored delay official is the news that Marvel Studios and Paramount will be releasing Kenneth Branagh’s Thor on Spider-Man‘s original release weekend, kicking off the summer on May 6, two weeks earlier than its original release plan.

According to Variety, Sony hasn’t abandoned the date yet and still hopes to get Spider-Man 4 done in time, but Paramount has decided to not wait and see what Sony does before grabbing that date themselves. They suggest that if Sony decides to keep that date then Thor will move again, although it’s doubtful they can get May 20 back again.

At this point, Sony hasn’t announced a new release date for Spider-Man 4. July 4th that year has been held for Michael Bay’s Transformers 3 followed two weeks later by the “Harry Potter” finale and then The First Avenger: Captain America, which hasn’t even announced its cast yet, the following week. (Warner Bros.’ Green Lantern has already grabbed June 17, potentially making it one of the busiest summers for comic book and superhero movies in some time.)

In related news, CineFOOLS reports that Thor will start filming this Friday!